Control system



June7, 1932. I w. R WICKERHAM 1,861,994

CONTROL SYSTEM Filed June 19, '1930 2 Sheets-Sheet 1 INVE NTOR7161111211: R. Wafer/1am 7 ATTORNEY J1me 1932- w. R. WICKERHAM 1,361,994

CONTROL SYSTEM Filed June 19, 1930 2 Sheets-Sheet 2 INVENTORMllz'amRWiaKez/mm A'TTQRNEY Patented June 7, 1932 UNITED STATES PATENTQFFICE;

WILLIAM R. WICKERHAM, OF \VILKINSBURG, PENNSYLVANIA, ASSIGNOR TOWESTING- HOUSE ELECTRIC & MANUFACTURING VANIA Application filed June 19,

My invention relates to hoisting machinery, and more particularly to anelectrical control system for operating the motor of a hoistgrab-bucket.

One of the objects of my invention is to provide for electricallycontrolling the closing and opening operations of the jaws of agrab-bucketby means of a simple electrical control system.

A further object of my inventionv is the provision of electrical meansmounted on the grab-bucket to close the jaws of the bucket, and byreason of my novel control system operate the jaws to closed position bysaid means a force not exceeding a predetermined value.

It is also an object of my invention to electrically limit the openingspeed of the jaws of the bucket when subject to a heavy overhaulingload, whereby damaging slack in the operating cables for the jaws andexcessive clashing of the jaws is prevented.

Other objects and advantages will be apparent from a study of thefollowing specification when taken in conjunction with the accompanyingdrawings, in which:

Figure 1 is a view in side elevation of a grab-bucket hoist.

Figs. 2 and 3 are perspective views of the grab-bucket showing theelectrical equipment mounted on the bucket; and,

Fig. 4 is a diagram of the electrical control system for controlling theoperation of the motor operating the jaws of the bucket.

Referring more particularly to Fig. 1 of the drawings, R designates arail along which the frame of the grab-bucket hoist is caused tooperatein a conventional manner. A pair of trolley wires 1 and 2 are disposedin parallel relation to the rail and constitute the source of directcurrent power for operating the electrical equipment mounted on thehoist frame and the grab-bucket.

Mounted on the frame is a motor 11 for operating the hoisting drum 12upon which a cable or chain 13 is arranged for lowering and raising thegrab-bucket 60 shown in Figs. 2 and 3. The power for operating the motor11 and the other equipment on the hoist frame is collected from thetrolley wires 1 and 2 by COMPANY, A- CORIOEATION OF PENNSYL- CONTROLSYSTEM 1930. Serial No. 462,222.

means of the trolley wheel-assemblage 3 and 4. A conduit 4' carries theelectric energy from the trolley wheel-assemblage to controller l4 andcontroller 9 located with controller 14 shown in the operatorsca'ge (seeFig. 1). The controller 9 is disposed to controlthe operation ofthemotor 11,.and the motor provided for actuating the hoist crane. Thecontroller 9 and the electrical equipment thereby controlled constituteno part of my invention and therefore need in full detail.

The controller 14 provided with a controller lever 14, controls theoperation of the elecnot be described trical equipment mountedintermediate the directional contactors 24, 26, 48 and 49 and a ruggedcopper ozide rectifier for selectively controlling the operation of themagnetically operated directional contactors, are all mounted on thegrab-bucket. A limit switch 52 is also mounted on the grab-bucket and isoperably associated with the cable 72 (see Fig.

4) for operating the levers 59 to close the jaws 61 of the grab-bucket.

The function of the limit switch 52 is to interrupt the circuit for themotor 56 and'to cause the locking of the brake mounted on thegrab-bucket. The limit switch is actuated either when the jaws havecompletely opened and a slack occurs in the cable 72 or when a slackoccurs. in the cable 72 because of the:

fact that the jaws have engaged an obstruction-and thus cannot open.

Motor 58 is a torque motor which operates the winding drum 57 for payingout the elec trical cable 21 and is so designed that it;

holds the cable 21 taut atall times, thereby preventing unnecessary wearon the cable and also possible rupture of the cable due to unusualoperating conditions. It is of course understood that winding drum 57may be operated by a spring mounted within the in fully closed orusually contained from four to five :conductors, and it is one of thenovelcharacteristics of my control system, that the cable for conductingthe electrical energy to the electrical 1 equipment on the grab-bucketcontains but two conductors. In consequence the" drum 57 and theoperating mechanisms associated with it may be relatively light andinexpensive.

. A more detailed understanding of my in vention may be had from adiscussion ofFig.

4. InFig. 4 the controllers .9 and '14 and the supporting structure 70are shown sche- ,zmatically in dotted lines. The elements 11,II'12,.57-,158,.56, 71, .etc.. refer to the elements....heretofore.discussedin connection to Figs. 1, i .2 and 3.

The operation of my control system to actuate the grab-bucket 60'is asfollows: Assum- .ingthat trolley wires 1 and 2-are supplied Lwith directcurrent volta e of a redetermined value,..then upon the closing of thesafetyswitch 8-the controller. 9 is energized anclwhen thecontrol lever9 is'actuated. the

hoisttrame may be caused to move along the 1 =rail R and themotor llmaybe caused to operate Motor 58, since it operates on the prin- ,ciple ofatorque motor is supplied with energy under constant conditions and isthus not sub- I hen-the safety switch 5 is closed and the j ect to anyspecial control.

. -segments of the controller 14 are actuated to the right,toxany-position .otherzthan position 6, a. circuitisestablishedwhichumay be traced from the positive trolley wire 1through trolley wheel 3, safety switch 5, over- ..:load circuit breakerF, actuating coil 16 of Ethe torque limiting. relay. 17, contact fingers18 bridged by the-controller segment 18,

= conductor. 19, slip ring 20, cable. 21, conductors 22 and 23, theactuating coils of the directional contactors 24; and 26, the copperoxideu'ectifier' 27, conductor 28, cable 21, slip :1 ring- 29, conductor30,-:contact fingers 31 bridged by the; controller-segment 31,contductor 32-,starting resistor 33, -conductor 34,

:overload' circuit breaker l3:-,sa-fety switch 5 and trolley wheel 4 tothenegatively energized trolley wire 2.

The copper'oxide rectifier 27 operates as an electric valve, permittingcurrent to flow only in the direction indicated by the arrow.Furthermore this rectifier is 'well known in the trade and is of veryrugged design, capa 'ble of withstanding severe shocks andother abusesin service over-long periods of time without undergoing any materialchanges in operating characteristics.

Immediately upon operation of directional contactors 24 and 26 a circuitis established which extends from the positively energized conductor22through thecoil of the magnetic brake 35, the seriesfield windings 36 ofthe motor 56, jamming resistor 37, conductor 38, the contact members ofthe directional conta'ctor 24,--conductor 39', the armature 40 ol -themotor 56, conductor 41, the contact members of the directionalcontactor' 26 to the negatively energized conductor 28. It will be notedthat during the closing operation of the jaws 61 of the grabbucket 60,the armature shunt resistor 54, is not connected in shunt relation tothe armature 40, but is connected shunt relation to the circuitextending from the junction 69 through the contacts of. the directionalcontactor 24 to the junction 68. 'Since this last traced circuit is oflow resistance value, .the effect of resistor 54 isunimportant.

Movement of the controller segment 42' to bridge the ..contact fingers.42, that is movement of the controller drum 14 tov position 6establishes a cir cuit which extends from'the right hand. terminal ofthe energized coil 16. through the contact fingers 42 bridged by the.controller. segment 42, the actuating coil of the accelerating ..relay..43, conductor 44, backcontacts of torque-limit relay 17 to thenegatively energized conductor 34. Operation ofthe accelerating relay 43establishes a. shunt .circuit for. the starting resistor 33. i

If during the closing of the jaws an obstruction is encountered by. thejaws, it is very desirable-that the jaws benot urged to closed positionby an excessive force, first, because of-the danger'to theelectricalequipment resulting from theheavy current-thus taken from theline and second, because it is usually desirablenot to' crush-:theobject intermediate the jaws. In the devices of the prior art, afriction clutch was genera lly provided which, during. the'condltionsjust specified, wouldslip and thuspermit continued rotation of themotor; It is thus obvious that mal-adjustment of thefriction clutch maynevertheless cause damage'to the motor and at the-same time crush theobject intermediate the jaws. -Further,ifthe friction'clutch beadjusted. tooloosely theob- 'ject intermediate-the aws may drop' afterhaving been hoisted toa considerable height with consequent. danger toattendantsv and workmen in the vicinity of the hoist.

To eliminate the. undesirable characteristics just outl-ined, I haveprovided the torque limiting relay 17. If, during a closing operation ofthe jaws, an obstruction is encountered and an excessive current istaken by the motor then the actuating coil 16 operates to open thebackcontact members of the object intermediate the edges of thejawswithout crushing the object and without drawing an excessive currentfrom the line. Closing of the upper contact members of the torque-limitrelay 17 merely establishes a holding circuit for the relay 17 throughthe coil 46, thereby preventing chattering of the relay.

During the stalling of the motor, as just explained, the voltageimpressed on the coils Y or the closing directional contactorsdecreases, but since these coils are connected in parallel circuitrelation with the coil of the magnetic brake 35, the series fieldwindings 36 and the amming resistor 37 connected in series, the voltageimpressed on the coils of the closing directional contactors issufficient to maintain the motor circuit.

During the opening operation of the grabbucket 60 the controller 14 ismoved to the left thereby. causing the bridging of contact fingers 53and 47 by controller segments 53' and 47. A. circuit is thus establishedwhich may be traced from the positively energized right hand terminal ofthe actuating coil'16 through contact fingers 47 ridged by thecontroller segment 47 conductor 30, slip ring 29, cable 21, conductor28, rectifier 27, the actuating coils of the opening directionalcontactor 4S and 49, conductor 50, contact members 51 of the limitswitch 52, conductor 22, cable 21, slip ring 20, contact fingers 53bridged by the controller segment 53, conductor 32, starting resistor 33to the negatively energized conductor 34.

Immediately upon 0 eration of the directional contactors 48 an 49 acircuit is established which extends from the positively energizedconductor 28 through the contact members of directional contactor 49,con ductor 39, armature 40, conductor 41, the contact members ofdirectional contactor 48, the jamming resistor 37, series field winding36 and the releasing coil of the magnetic brake to the negativelyenergized conductor 22. It will be noted that the resistor 54 isconnected in parallel circuit relation with the armature and inconsequence the speed of the motor during the opening operation,especially if the load is overhauling, is limited to a safe value.

lVhen the jaws 61 of the bucket have opened completely and also when theopening of the jaws is prevented by an obstruction, a slack occurs incable 72 whereby the limit switch 52 is permitted to operate to open thecircuit for the directional contactors 48 and 49, which in turn "causesan interruption of the energy supplied to the motor 56 and locking ofthe magnetic brake 35.

The motor 56 is accelerated in the opening direction in the same manneras it is accelerated in the closing direction, since movement of thecontroller segment 42" to bridge contact fingers 42 energizes theaccelerating relay 43 which in turn establishes a shunt circuit for thestarting resistor 33.

While the foregoing disclosure sets forth with particularity the circuitconnection inherent in my invention and discloses the combination ofthese connections with the grabbucket and the means for operating thegrab-bucket, I do not wish to be limited to the specific detailsdisclosed but wish-to be limited only by the appended claims. I

I claim as my invention .1. A motor control system for an electricallyoperated grasping device, a grasping device, electrical devices mountedon the grasping device and including a motor for operating the graspingdevice, a contactor for connecting the motor to cause opening of thegrasping device, a limit switch for causing the interruption of theconnections established by the contactor when thegrasping device failsto open in response to the normal torque of the motor and a magneticbrake for holding the operated parts of the grasping device in theposition to which they were moved by the motor at the instant of theoperation of the limit switch.

' 2. In a control system for a motor mounted on a grab-bucket havingjaws, means responsive to a predetermined overload on the motor duringthe closing of the jaws, caused either by the fact that the jaws havecompletely closed or by the fact that the jaws have encountered anobstruction during closing, for reducing the armature current of themotor to cause operation of the motor on the principle of a torque motorto hold the jaws against the obstruction or in closed position.

3. In a motor control system for an electrically operated grab-bucket,in combination, a grab-bucket, electrical devices mounted on the bucketand including a motor for opening and closing the bucket, closingcontactors, opening contactors, a limit switch in series with theopening contactor and responsive to abnormal opening conditions of "foropening and closing the :bucket and-clos I wing. contactors forconnectmg the motor to i came closing of the grab-bucket, a pair ofconductors leading from the electrical devices, supply lines forsupplying electric energy and a controller disposed-for operation toselectively connect the supply lines to 5. A motor control system for anelectrically ooerated Tab-bucket havin aws com-- "I w b n u b prising,in combination, a motor mounted on the grab-bucket for opening andclosing the grab-bucket, a palr of conductors-leading from the motor,supply lines for supplying electric energy, a controller remote from themotor for selectively connecting thesupply lines to the conductorsthereby causing open- 1 ing or closing of the grab-bucket depending onthe connection selected by the controller,

said controller including a starting resistor,

means responsive to a predetermined over load on the motor during theclosing of the jaws caused by an obstruction encountered" by the jaws orby the fact that the jaws have completely closed, for connecting thestarting resistor in series with the motor thereby pausing the aws to beheld in closed position against the action of the motor operating on theprinciple of a torque motor.

6. In a control system for an electrically operated grab-bucket,electrical devices mounted on the grab-bucket and including a motor foroperating the grab-bucket, a reversing contactor unit,aresistor'connected in series circuit relation withthe motor, saidreversing contactor unit being connected in )arallel with the motorwhereb the reversing contactor unit is maintained energized regardlessof changes in counter-electromotive force of the motor, a magnetic brakeand an electric valve for selectively controlling the re\'*ersingcontactor unit, a source of power, two conductors leading from the source ofpower and a double throw controller for selectively connectingthe twoconductors to the source of power, said controller including a resistor,means for shunting the resistor and means responsive to a predeterminedoverload on the motor for deenergizing the resistor shunting means.

7. In a control system for an electrically operated grab-bucket havingjaws, and having mounted thereon a motor for opening and closing thejaws, a magnetic brake, and

a resistor connected in series circuit relation with the motor, openingd1rect1onalcontactors and closing directional contactors in parallelwith the motor, brake and 'IBSlStOI,

. the resistance drop across the resistor when sub ect to-normaloperating voltage being sufficient to prevent the opening ofthedirectional'contactor when in closed position, a speed control resistorarranged to be'connected in: parallel with. the motor armature when themotor is operating to open-thejaws of the'grab-bucket: therebypreventing excessive speeds in the opening direction.

8; Ina control system '-f0ri an electrically operated bucket having amovable aw, electrical devices mounted on the bucket and including, amotor for operating the-jaw, a contactor having contact members forc011- necting the motor to operate the jaw-and a -resistor connected inseries-circuit relation with the motor, said cont'a'ctorpbeing"con;nectedito be responsive'to the resistance'drop across the resistor toprevent the actuation of the contact members to their OPGIIPQSltlOII, acontroller, conductors connectmg electrical devices to the controller,means res onsive to. overload on the motor; for limiting thecurrentdrawn by the motor whereupon thej aw is actuated by the motor operatingon. the: principle of a torque motor.

9. In a control system for an electrically operated bucket, electricaldevices mounted on the bucket and including a motor, a magnetic;brake,'current limiting means: for-:limitingthe motor current when themotor 1s operating 1n one direction, means for limitingthe speed of themotor when operating .in the opposite d1rect1on,.a reversing contactorunit and an electrlc valve for selectively controlxling the energizationof the reversing. contactor unit, two conductors connected to'the'".electrica-l devlces, a reel for the conductors'to maintain them taut, asource of power and a controller for connectmg the source ofpower to theconductors, current l1m1t1ng means mounted on the controlleroperating'jointly and additively with the current-limiting device on thebucket.

In testimony whereof, I have hereunto'subscribed my name this 17th dayJun'e; =1930.

WILLIAM R. I/VIGKERH AM.

